**4.2. NPs targeting DC for delivering cancer vaccines**

on cancer vaccines that were combined with other elements, such as potent adjuvants and NP-based VADSs. For example, in a preclinical study, researchers observed that, in a syngeneic mouse model of oral cancer comprised of mouse tonsil-derived epithelial cells stably expressing HPV-16 E6 and E7 genes along with H-ras oncogene (mEER), intranasal HPV E6/E7 peptide vaccination or single checkpoint antibodies failed to elicit responses in most mice; however, 4-1BB agonist antibody along with either CD40 agonist antibody or CTLA-4 blockade eliminated the majority of established mEER tumors, and even produced a curative efficacy and a high safety profile against orally implanted mEER tumors [40]. For another example, in a phase II clinical trial, researchers performed immunotherapy with two peptide cancer vaccines in combination with intravesical bacillus Calmette-Guerin (BCG) for patients with non-muscle invasive bladder cancer (NMIBC) and demonstrated that this combinatory immunotherapy had good immunogenicity and safety and resulted in a 2 year RFS rate 74.0% in all patients, suggesting the cancer vaccines with a combinatory mode may provide benefit

These investigations showed that the conventional vaccines have limited capability to target delivery of tumor Ags and adjuvants to proper APC and intracellular compartments and may be renovated by the NP-based vaccine adjuvant-delivery systems (VADSs) which have

Cancer immunotherapy by vaccines depends on eliciting in patient the antitumor adaptive cellular immunity, which is, however, governed by potent Ag-presenting DCs able to activate CD8+ T cells and engender the Ag-specific CTLs. For this purpose, various immunotherapy strategies have been developed, including, in particular, using NP-based VADSs that are so elaborately designed as to promote APC cross-presentation of Ags and to deliver Ags and/or adjuvants targeting APCs, tissues, or organs such as dLNs, wherein APCs aggregate in large number ready for uptake of foreign substances, as can hardly be accomplished by soluble Ags

During an immune response, exogenous Ags are usually processed and presented via MHC-II by APCs to CD4+ T cells; however, tumor Ags engulfed by APCs require to be presented via MHC-I to induce production of Ag-specific CTLs, which are the main effector cells against tumor cells, thus precluding traditional methods from engineering cancer vaccines as they rely on soluble protein or peptide tumor Ags which often skew immune responses to CD4+ T cell responses while failing to induce robust CTL responses which are sufficient for cancer immunotherapy. Fortunately, it is disclosed that tumor Ags delivered by the elaborately designed NP-based multifunctional VADS able to promote lysosome escape, which is translocation of Ags from endosomes or phagosomes to cytosol avoiding Ag degradation within lysosomes, may regulate Ags to be reloaded to endoplasmic reticulum (ER)-attached MHC-I

to patients for preventing recurrence of NMIBC [41].

52 Immunization - Vaccine Adjuvant Delivery System and Strategies

**4. NPs delivery of cancer vaccines**

or adjuvants alone [12].

already poised to address these challenges as described below.

**4.1. NPs promoting Ag cross-presentation for delivering cancer vaccines**

Recently, the approach based on amphiphilic polymer-Ag peptide conjugates through the conjugation of azide-functionalized Ag peptides to an alkyne-functionalized core via azidealkyne click chemistry has been employed for making nanovaccines against cancer. For example, by conjugation of the melanoma Ag peptide TRP2 and azido PEG mannose to the alkyne polymer, an anti-melanoma nanovaccine with the size of 10–30 nm was formed via self-assembly and was efficiently taken up by DCs [47]. In spite of poor immunogenicity, when given to model mice with B16-F10 melanoma tumors together with the adjuvant CpG, the adjuvanted TRP2-nanovaccines effectively suppressed the tumor growth and significantly improved the survival of mice compared to the untreated group. Moon's group engineered synthetic high density lipoprotein (sHDL) nanodiscs consisting of phospholipids, apolipoprotein A1 (Apo A1)-mimetic peptides and cholesterol-conjugated CpG (sHDL-Ag/CpG) with average diameter of 10 ± 0.5 nm, which were used as a multifunctional VADS able to target lymphoid organs, resulting in sustained Ag-presenting on DCs [48]. Moreover, the sHDL-CpG-based VADS loaded with multiple Ags (MHC-I-restricted M27, MHC-II-restricted M30, and TRP2) in combination with anti-PD1/anti-CTLA4 antibodies successfully rejected B16- F10 tumor from tumor-bearing mice.

for efficient targeting to professional APCs, which may be well obtained through formulating into the NP-based VADSs. This has been accomplished by dextran-CpG-OVA conjugate that enhanced not only the CD8+ T cell responses but also improved the antitumor immunotherapy through whole tumor cell vaccine. Recently, Liu and coworkers using reductive amination method conjugated oxidized dextran to amine-modified CpG ODN and demonstrated that the dextran-CpG conjugate with a hydrodynamic diameter of 6.5 nm was accumulated dLNs and was efficiently taken up by mouse DCs [53]. With the combination of OVA as a model Ag, dextran-CpG conjugate elicited production of Ag-specific CD8+ T cells for effective therapeutic benefits and in subcutaneously immunized mice resulted in significant reduction of tumor growth and increased survival of

Vaccines Developed for Cancer Immunotherapy http://dx.doi.org/10.5772/intechopen.80889 55

To induce a potent MHC-I-restricted CTL response which is an essential component of the successful cancer immunotherapy treatment, Huang's group formulated the mannosylated lipid-calcium-phosphate (MLCP) NPs as a new class of intracellular delivery systems for cytosol delivery into DCs of an exogenous Ag, p-Trp2 (the melanoma Ag Trp2 peptide derivative bearing two phosphor-serine residues) [54]. Compared with free Trp2 peptide/ CpG ODN, MLCP NPs encapsulation enhanced and prolonged the cargo deposit into the lymph nodes (LNs) and also resulted in superior inhibition of tumor growth in both B16F10 subcutaneous and lung metastasis mouse models owing to induced IFN-γ production and a Trp2-specific CTL immune response. Thus, encapsulation of phospho-peptide Ags into LCP may be a promising strategy for enhancing the immunogenicity of poorly immunogenic self-

Recently, a nanovaccine, called AlbiVax that is assembled in vivo from endogenous albumin nanocarriers and exogenous molecular vaccines, which are chemically defined and relatively well suited to large-scale production including quality control and safety evaluation, has been developed based on the albumin properties which are well known of not only being efficiently internalized by APCs via endocytosis to facilitate intracellular vaccine delivery for optimal Ag processing and presentation but also binding to a clinically practiced Evans blue (EB) [55]. AlbiVax was synthesized by conjugating thiol-modified vaccines and adjuvants, such as the 3′-end thiol-modified CpG and Ags (CSIINFEKL, Trp2, and Adpgk) modified with N-terminal cysteine, with maleimide-functionalized EB derivative which can tightly bind to human serum albumin. Further investigation revealed that, compared to benchmark incomplete Freund's adjuvant (IFA), AlbiVax had a much high efficiency in co-delivery of CpG and Ags to LNs and in eliciting peripheral Ag-specific CD8+ CTLs with immune memory and specifically inhibited progression of established primary or metastatic EG7.OVA, B16F10, and MC38 tumors; but only in combination with anti-PD-1 and/or Abraxane did AlbiVax eradicate most MC38 tumors. These outcomes indicate that as a novel type of VADS, the in vivo self-assembled molecular nanovaccines can not only enhance vaccine bioavailability in LNs but also bypass the complications, such as inefficient delivery, sequestering Ag determinant-specific T cells in the depots, and exhausting and depleting T cells, thereby preventing T cells from infiltrating tumors and difficulty in large-scale production, which are often associated with

mice.

Ags for cancer therapy.

conventional synthetic vaccines [56].

Though targeting delivery with NPs is able to improve efficacy of cancer vaccines, tumorinduced DC dysfunction arising from hyperactivity of signal transducer and activator of transcription 3 (STAT3) [49], which leads to less maturation in DCs with low responsiveness to pattern recognition receptor agonist (PRRa) stimulation [50], engenders another major huddle to developing effective vaccines for cancer immunotherapy. The NPs-based VADS was trialed in overcoming tumor-induced DCs dysfunction by Ma and colleagues through using poly(ethylene glycol)-b-poly(L-lysine)-b-poly(L-leucine) (PEG-PLL-PLLeu) to form 120 nm-sized polypeptide micelles for encapsulation of polyI:C, STAT3 siRNA, and OVA as a nanovaccine (PMP/OVA/siRNA), which proved able to decrease STAT3 expression and increase CD86 and CD40 expression as well as IL-12 production [51]. Moreover, PMP/OVA/siRNA nanovaccine could effectively increase mature DCs and decrease immunosuppressive cells in tumor draining lymph node, leading to antitumor immune response and prolonged survival, implying that novel VADSs designed for codelivery of immunopotentiator and immunosuppressive gene silencer may be one of potent strategies to improve antitumor immunity by modulating tumor-induced DCs in tumor microenvironment.
